Acronym pronounced as word with short i sound. (I)dentification (F)riend or (F)oe - (S)ecure (I)dentification (F)eature. Technology developed during the Cold War period for identifying and authenticating otherwise unknown aircraft as friend or foe (delivering, maybe, gadzooks!! an atom bomb!). Used in modern aviation to positively identify airliners inflight with a code that's normally assigned to each flight, along with its flight plan clearance, on the ground. It automatically sends a periodic electronic signal to ATC radars, or can be activated manually when a pilot is asked to squawk ident. Also known as a transponder, as it transmits a response (the assigned code) to Air Traffic Control when ATC specifically signals for it.